Fresh new start using Marionette

* Deletes old Backbone based models, collections and views.
* Adds dependency gems to Gemfile.
* Adds dependency libraries to assets/javascripts/lib directory.
* Edits root_url.
Creates CustomersController to link to Customer model from Backbone

* Creates CustomersController to return json only.
* Defines WelcomeController#index to return empty page.
Bootstrapping first two Marionette Sub-Apps

* Creates Badi Marionette App.
* Creates DashboardApp module to handle all dahsboard related activities.
* Creates CustomersApp module to handle routing for Customers.
* Creates CustomersApp.List module to handle common index action for
  Customers with Marionette.
* Creates CustomersApp.List views to display table with existing
  customers for logged in user.